Question about mulching around tree trunks - Ask Extension
Hello, I recently saw some kind of a public announcement video about “tree volcanoes“ meaning people that pile lots of mulch around a tree trunk. ...
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Question about mulching around tree trunks #915537
Asked August 27, 2025, 10:13 AM EDT
Hello, I recently saw some kind of a public announcement video about “tree volcanoes“ meaning people that pile lots of mulch around a tree trunk. The video stated that doing so would cause the roots to start growing up to the surface to seek oxygen. Is this true?
I do understand that piling mulch around a tree at a very high level is not good for the tree, but I want to understand all of the biological reasons… Thank you, sincerely, Betsy Godwin
Cook County Illinois
Expert Response
Yes, as muscles start to compact and break down, it can reduce the amount of oxygen that is able to get to the roots in the soil. In response to this, trees may start growing new roots in the mulch where oxygen levels are higher. Over time, these roots can become exposed as the mulch continues to break down, causing them to dry out and potentially die.
Having mulch piled up against the trunk of the plant can also lead to decay, because the mulch will retain moisture, allowing pathogens to attack the bark of the tree.
Having mulch piled up against the trunk of the plant can also lead to decay, because the mulch will retain moisture, allowing pathogens to attack the bark of the tree.
